1. Field of the Invention
The present invention relates to a method of filtering a fluid, and more particularly, to a method of removing, from a fluid, very minute objects of removal measuring 0.1 xcexcm or less.
2. Description of the Related Art
At present, diminishing the amount of industrial waste, separate collection and recycling of industrial waste, and prevention of release of industrial waste are considered to be ecologically-important topics and business issues as society moves toward the Twenty-first century. Some types of industrial waste comprise various types of fluids containing objects of removal; i.e., substances to be removed.
Such fluids are known by a variety of expressions, such as sewage, drainage, and effluent. Fluids, such as water or chemicals, containing substances which are objects of removal will be hereinafter referred to as xe2x80x9cwastewater.xe2x80x9d The objects of removal are eliminated from wastewater by means of an expensive filtration system or a like system. Thus, wastewater is recycled as a clean fluid, and the removed objects of removal or substances which cannot pass through the filtration system are disposed of as industrial waste. Particularly, water is sent back to a natural setting, such as a river or the sea, or recycled after having been purified so as to meet environmental standards.
Adoption of such a filtration system is difficult because of costs incurred in constructing and running a filtration system, thus posing an environmental problem.
As can be seen from the above description, a technique for disposing of wastewater is important in terms of recycling and prevention of environmental contamination, and immediate demand exists for a filtration system incurring low initial and running costs.
By way of illustration, there will now be described disposal of wastewater as practiced in the semiconductor industry. When a plate member formed from, for example, metal, a semiconductor, or ceramics, is ground or abraded, an abrasion (or grinding) jig or the plate member is subjected to a shower of a fluid, such as water, for preventing an increase in the temperature of the abrasion (or grinding) jig, which would otherwise be caused by friction, for improving lubricity, and for preventing adhesion of abrasion or grinding waste to the plate member.
More specifically, at the time of dicing or back-grinding of plate-like semiconductor material; e.g., a semiconductor wafer, pure water is caused to flow over the semiconductor wafer. In a dicing machine, a shower of pure water is caused to flow over a semiconductor wafer, or pure water is squirted onto a blade from a discharge nozzle, in order to prevent an increase in the temperature of a dicing blade or adhesion of dicing waste onto the semiconductor wafer. For the same reason, a flow of pure water is employed during an operation in which a semiconductor wafer is made thin by means of a back-grinding operation.
Wastewater which has mixed therein grinding or abrasion waste and is discharged from the dicing or back-grinding machine is returned to a natural setting or recycled after having been purified through a filter. Alternatively, concentrated wastewater is collected.
In a current process for manufacturing a semiconductor, wastewater in which objects of removal (i.e., waste) primarily consisting of silicon are mixed is disposed of according to either of two methods; i.e., a coagulating sedimentation method and a method which employs a filter and a centrifugal separator in combination.
Under the coagulating sedimentation method, polychlorinated aluminum (PAC) or aluminum sulfate [Al2(SO4)3] is mixed into wastewater as a coagulant so as to react with silicon, to thereby form a reactant. The wastewater is filtrated by removal of the reactant.
Under the method which employs a filter and a centrifugal separator in combination, wastewater is filtrated, and concentrated wastewater is processed by a centrifugal separator, thereby collecting silicon waste as sludge. Clear water resulting from filtration of wastewater is released to a natural setting or recycled.
For example, as shown in FIG. 18, wastewater discharged during a dicing operation is collected into a raw water tank 201 and is sent to a filtration unit 203 by means of a pump 202. A ceramic-based or organic-based filter F is provided in the filtration unit 203, and hence which has been water filtrated through the filter F is delivered, by way of a pipe 204, to a collected water tank 205 wherein the water is recycled. Alternatively, the filtrated water is released to a natural setting.
In the filtration unit 203, wastewater is supplied to the filter F under pressure, thus clogging the filter F. To eliminate clogging of the filter F, the filter F is periodically cleaned. For instance, a valve B1 connected to the raw water tank 201 is closed, and there are opened a valve B3 and a valve B2 for delivering collected water from the collected water tank 205. The water supplied from the collected water tank 205 is used for cleaning the filter F. The resultant wastewater containing a high concentration of silicon waste is returned to the raw water tank 201. Concentrated water in a concentrated water tank 206 is transported to a centrifugal separator 209 by way of a pump 208. In the centrifugal separator 209, the concentrated water is separated into sludge and a separated fluid. Sludge consisting of silicon waste is collected into a sludge recovery tank 210, and the separated fluid is collected into a separated fluid tank 211. After a separated fluid has been further accumulated in the separated water tank 211, the separated fluid is transported to the raw water tank 201 by way of a pump 212.
These methods have been employed even for recapturing waste resulting from grinding or abrasion of a solid or plate-like substance formed essentially from metal material; for example, Cu, Fe, or Al or from grinding or abrasion of a solid or plate-like substance formed from an inorganic substance such as ceramic.
A chemical-and-mechanical polishing (CMP) technique has been adopted as a new semiconductor processing technique. The CMP technique is for smoothing the upper surface of an interlayer dielectric film covering an interconnect in order to materialize an ideal multilayer interconnect structure, wherein irregularities formed in the upper surface of an interlayer dielectric film are chemically and mechanically abraded away.
The CMP technique enables materialization of a smooth device surface. As a result, a minute pattern can be accurately formed on the device through use of the lithography technique. Use of the CMP technique in conjunction with a technique of affixing silicon wafers enables materialization of a three-dimensional integrated circuit.
Second, the CMP technique enables materialization of a structure in which there is embedded material differing from a substrate, thus yielding an advantage of facilitated realization of an embedded interconnect structure. There has been employed a technique of embedding tungsten (W) in a trench of an interlayer film of multilayer interconnect of an IC by means of the CVD technique. The thus-embedded interlayer film is etched back, thus smoothing the surface of the interlayer film. However, smoothing an interlayer film by means of the CMP technique yields an advantage of facilitating a process, and hence the CMP technique has recently come into the limelight.
The CMP technique and applications thereof are described in detail in a periodical entitled xe2x80x9cScience of CMPxe2x80x9d issued by a science forum.
The mechanism of a machine used for CMP will now be briefly described. As shown in FIG. 19, a semiconductor wafer 252 is placed on an abrasive cloth 251 placed over a rotary table 250. The semiconductor wafer 252 is abraded by being slid over the abrasive cloth 251 while an abrasive (i.e., slurry) 253 is caused to flow over the surface of the semiconductor wafer 252. Further, the semiconductor wafer 252 is chemically etched, thereby eliminating irregularities from the surface of the wafer 252. More specifically, the semiconductor wafer 252 is abraded by means of chemical reaction induced by a solvent included in the abrasive 253, as well as by means of mechanical abrasive action effected by the abrasive cloth 251 and the abrasive 253. Expanded polyurethane or non-woven fabric, for example, is used as the abrasive cloth 251. Further, the abrasive corresponds to a mixture comprising abrasive grains, such as silica or alumina, and water containing a pH regulator. The abrasive is usually called slurry. The semiconductor wafer 252 is brought into slidable and rotatable contact with the abrasive cloth 251 while predetermined pressure is applied to the semiconductor wafer 252 and the slurry 253 is caused to flow over the abrasive cloth 251. Reference numeral 254 denotes a dressing section for maintaining the ability of the abrasive cloth 251 to abrade and keeping the surface of the abrasive cloth 251 in a finished (or dressed) state at all times. Here, reference numerals M1 to M3 designate motors, and reference numerals 255 to 257 designate belts.
As shown in FIG. 20, the mechanism is constructed as a system. The system is roughly divided into a station 260 for loading/unloading a wafer cassette, a wafer transport mechanism section 261, an abrasive mechanism section 262 which has been described by reference to FIG. 19, a wafer cleaning mechanism section 263, and a system controller for controlling these sections.
A cassette 264 having wafers stored therein is disposed in the station 260, and a wafer is taken out of the cassette 264. In the wafer transfer mechanism section 261, the wafer is retained by, for example, a manipulator 265, and is placed on the rotary table 250 disposed in the abrasive mechanism section 262. The wafer is then smoothed by means of the CMP technique. After smoothing of the wafer has been completed, the wafer is transported by means of the manipulator 266 to the wafer cleaning mechanism section 263 wherein the wafer is cleaned. The thus-cleaned wafer is housed in the wafer cassette 264.
The amount of slurry used for one abrasion process is about 500 c.c. to 1 liters/wafer. In the abrasive mechanism section 262 and the wafer cleaning mechanism section 263, pure water flows. The wastewater flowing out of the abrasive mechanism section 262 and the wastewater flowing out of the wafer cleaning mechanism section 263 are finally merged into a single effluent in a drain. Wastewater in an amount of about 5 to 10 liters/wafer flows out during a single smoothing operation. In the case of producing, for example, a wafer of three-layer metal, about seven smoothing operations are required for smoothing metal and interlay dielectric films. For production of a single wafer, wastewater flows out in the amount of seven times the 5 to 10 liters flowing in manufacturing a single IC device completely.
Use of a CMP machine involves discharge of slurry of a considerable amount diluted with pure water, thus posing a difficulty in efficient treatment of wastewater. The wastewater has conventionally been treated by the coagulating sedimentation method or the method which uses a filter and a centrifugal separator in combination and is shown in FIG. 18.
Under the coagulating sedimentation method, a chemical is used as a coagulant. Specifying the amount of chemical which attains complete reaction with objects of removal is very difficult, and hence a large mount of chemical is discharged into the wastewater, so that chemical which has not reacted with wastewater remains. If the amount of chemical is insufficient, not all the objects of removal are coagulated and settled out, so that some of the objects of removal remain unseparated. In a case where a chemical is used excessively, the chemical remains in a supernatant liquid. In a case where the supernatant liquid is recycled, chemical remains in a fluid which has passed through a filter. Hence, the thus-filtered fluid cannot be used for an application in which occurrence of a chemical reaction is to be avoided.
In the case of dicing of a silicon wafer, wastewater comprises silicon waste and distilled water. The water that has been filtrated by the coagulating sedimentation method still contains chemical residue. Therefore, if the thus-filtrated water is applied to a wafer, an undesirable chemical reaction will occur. For this reason, the filtrated water cannot be recycled as water to be used in a dicing operation.
A floc resulting from a reaction between a chemical and an object of removal corresponds to a tuftlike suspended solid. Production of such a floc is achieved under strict pH conditions and requires control equipment for controlling an agitator, a pH measurement instrument, and a coagulant injection apparatus. Stable sedimentation of a floc requires a large-size precipitation tank. For instance, a precipitation tank having the ability to treat wastewater at 3 cubic meters/hour requires a diameter of 3 meters and a depth of about 4 meters (i.e., corresponds to a precipitation tank having a capacity of about 15 m3. As a result, there is required floor space or round space measuring about 11xc3x9711 meters, thus rendering the scale of the entire filtration system large.
Further, some flocs float on the surface of wastewater and may flow out of the precipitation tank. Thus, recovery of all flocs is difficult. In short, the known filtration system suffers problems; i.e., the size of a facility, high initial costs required by the system, a difficulty in recycling water, and high running costs incurred by use of a chemical.
Under the method, such as that shown in FIG. 18, which employs a filter having a capability of filtrating 5 cubic meters/hour and a centrifugal separator in combination, the filtration unit 203 uses a filter F (called UF module comprising a polysulfon-based fiber or a ceramic filter), thereby enabling recycling of water. The filtration unit 203 is equipped with four filters F. In view of life of the filters F, the filters F must be replaced with high-priced filters, each costing about 500,000 yen, every year. Further, since the filter F is for use with a pressure filtration method, the pump 202 disposed upstream of the filtration unit 203 must have a high capacity. About two-thirds the wastewater which has passed through the filter F is returned to the raw water tank 201. Further, wastewater containing objects of removal is transported by the pump 202, and hence the interior wall of the pump 202 is scraped by the objects of removal, thus greatly shortening the life of the pump 202.
As mentioned above, the known filtration system suffers high running cost; specifically, electricity consumed by a motor and expenditures required for replacing the pump and the filters F with new ones.
Further, the amount of wastewater discharged during a CMP operation cannot compare with that discharged during a dicing operation, and the abrasive grains mixed in a slurry are very minute and comprise grains of 0.2 xcexcm, grains of 0.1 xcexcm, and grains of 0.1 xcexcm or less. If such fine abrasive grains are filtrated through use of a filter, the abrasive grains enter pores of the filter, thus frequently clogging the filter and making disposal of a large amount of wastewater impossible.
As can be seen from the foregoing description, in order to eliminate a maximum amount of substances harmful to the global environment and recycle a filtrated fluid or separated objects of removal, various devices are added to the effluent filtration apparatus, thus constituting a large-scale filtration system. Eventually, the system involves enormous initial cost and running cost. For these reasons, the known sewage treatment plant cannot be adopted.
The present invention has been conceived in view of the foregoing problems of the related art and is aimed at providing a sewage treatment method which enables a reduction in initial cost and running cost.
The present invention is also aimed at eliminating objects of removal from a fluid (i.e., wastewater) having mixed therein objects of removal, such as a semiconductor, metal, an inorganic substance, or an organic substance, through use of a filter formed from a solid substance differing from the objects of removal.
The present invention is also aimed at removing objects of removal from a fluid by mixing solid substances into the fluid and causing the fluid to pass through a first filter, to thereby constitute over the surface of the first filter a second filer including the solid substances.
The present invention is also aimed at removing objects of removal from a fluid through use of a filter formed from solid substances differing from the objects of removal.
The present invention is also aimed at removing objects of removal from a fluid by introducing, into a tank having a first filter, a fluid containing the objects of removal and solid substances differing from the objects of removal and by causing the fluid to pass through the first filter, to thereby constitute over the surface of the first filter a second filer containing the solid substances.
Herein, a term xe2x80x9cobjects of removalxe2x80x9d designates solid matter contained in wastewater to be filtrated. The solid substance designates a substance constituting a filter film which is for filtrating wastewater containing objects of removal and is formed by collection of solid matter, such as sand. For example, the solid substance is to be formed into a layer over a first filter film. Therefore, the solid substance preferably has a filtration performance higher than that of the first filter film and is preferably separated into pieces upon receipt of external force.
More specifically, the objects of removal contain a large quantity of grains of about 0.3 xcexcm, grains of 0.2 xcexcm, and grains of 0.1 xcexcm or less. For instance, the objects of removal contain abrasive grains used for a CMP operation, waste semiconductor material resulting from grinding of a semiconductor material with the abrasive grains, metal waste and/or waste material for a dielectric film.
The objects of removal correspond to waste arising when a crystalline ingot is sliced into wafers, when a semiconductor wafer is diced, and when a semiconductor wafer is subjected to back-grinding. Primarily, the objects of removal correspond to semiconductor material, insulating material, metal material, silicon (Si), silicon oxide, aluminum, SiGe, an organic substance such as a sealant, another insulating film material, or a metal material. In the case of a compound semiconductor, a compound semiconductor material, such as GaAs, corresponds to an object of removal.
A dicing technique has recently been employed for manufacturing a chip-size package (CSP). Semiconductor material, ceramic material, and sealant, which would arise during the dicing of a wafer, also correspond to an object of removal.
Objects of removal arise in various industries other than the semiconductor industry. For example, in industries using glass, formation of a panel, such as a liquid-crystal panel or an electroluminescence (EL) display, involves dicing of a glass substrate and abrasion of side surfaces of a substrate. Therefore, in this field, glass waste corresponds to objects of removal. Further, power companies and steel producers use coal as fuel, and fine particles originating from coal correspond to objects of removal. Further, fine particles mixed in smoke emitted from a smoke stack also correspond to objects of removal. Fine particles resulting from machining of minerals, gems, and gravestones also correspond to objects of removal. Further, metal waste resulting from lathing of metal and ceramic waste resulting from dicing or abrasion of a ceramic substrate also correspond to objects of removal.
These types of waste are produced when material is subjected to machining, such as abrasion, grinding, or pulverization. In order to remove the waste, the waste is mixed into a fluid, such as water or a chemical, thus producing wastewater.
Solid substances correspond to substances which are distributed over a range of particle size (about 500 xcexcm ) wider than a distribution of particle size (about 0.14 xcexcm ) of objects of removal (i.e., abrasive grains used for a CMP operation) For example, solid substances correspond to semiconductor material, such as Si; grinding, abrasion, or pulverized waste, such as metal; or solid substances having a distribution equal to the above-described distribution of particle size; for example, diatomaceous earth or zeolite.
In the present invention, objects of removal are removed from a fluid through use of a filter containing solid substances differing from the objects of removal.
Further, objects of removal are removed from a fluid through use of a filter containing solid substances whose distribution of particle size is wider than that of the objects of removal.
Further, objects of removal are removed from a fluid by mixing solid substances into the fluid and causing the fluid to pass through a first filter, to thereby constitute over the surface of the first filter a second filter containing the solid substances.
In order to eliminate a particulate matter of 0.1 xcexcm, such as an abrasive grain to be mixed into a slurry for use in a CMP operation, a filter film having pores smaller than the particulate matter is generally employed. However, in the present invention, a solid substance which is substantially equal in size with or greater in size than an object of removal is formed into a layer on the surface of the first filter, to thereby constitute a second filter film. A plurality of apertures formed in the second filter film are utilized as passages for a fluid. In the present invention, the second filter per se is a cluster of solid substances. Therefore, objects of removal and a surface layer of solid substances, which would cause clogging, can be spaced from the second filter film, thus maintaining the filtration ability of the second filter film.
In the present invention, objects of removal are removed by mixing into a fluid solid substances which are greater in diameter than those of the objects of removal and causing the fluid to pass through a first filter, to thereby constitute over the surface of the first filter a second filter containing the solid substances.
Use of the first filter enables formation over the first filter of a second filter film to be formed from solid substances. The second filter film removes objects of removal.
In the present invention, objects of removal are removed from a fluid through use of a filter formed from solid substances differing from the objects of removal contained in the fluid.
Further, after a filter has been formed from solid substances differing from objects of removal contained in a fluid, the objects of removal are removed from the fluid through use of the filter.
Further, a first filter is immersed in a fluid, and solid substances differing from objects of removal contained in the fluid are caused to pass through the first filter, to thereby constitute over the surface of the first filter a second filter containing the solid substances. Thereafter, a fluid containing the objects of removal is caused to flow through the first and second filters, thus removing the objects of removal from the fluid.
So long as a filter containing solid substances is prepared beforehand, a fluid stored in a tank can be filtrated immediately. Further, a second filter can be formed within the fluid. If a fluid containing objects of removal is caused to flow through the second filter, formation of the second filter and filtration of a fluid through the second filter can be carried out continuously.
A fluid containing objects of removal and solid substances differing from the objects of removal is introduced into a tank having a first filter, and the fluid is caused to pass through the first filter, thereby constituting over the surface of the first filter a second filter containing the solid substances. Thus, the objects of removal are eliminated from the fluid.
If the second filter film is formed from only objects of removal, the second filter film is formed to have small filter pores, so that the filtration capability of the second filter film is deteriorated. However, if solid substances are mixed into the second filter film, apertures of various sizes are formed in the second filter film, thereby enabling an increase in the rate of filtration of a fluid.
Since the fluid is acidic or alkaline, a neutralizer is mixed into the fluid, thus neutralizing the fluid.
Preferably, the fluid is caused to circulate through the filter or the first filter. As a result of circulation of the fluid, the objects of removal contained in the fluid and solid substances accumulate as a second filter film having the capability of capturing objects of removal of a predetermined particle size.
Preferably, the filter or the second filter contains solid substances or objects of removal of different sizes.
Particularly, so long as solid substances of different sizes are employed, the solid substances are randomly stacked into layers, thus increasing the number of apertures and constituting apertures of different sizes. Consequently, flow channels for a fluid can be ensured, thus increasing the rate of filtration of a fluid.
The solid substances or the objects of removal contain particles of different sizes, and the pores of the first filter are greater in size than the smallest grain and smaller in size than the largest grain.
The diameter of the smallest solid substance or objects of removal is less than 0.25 xcexcm, and the diameter of the largest solid substance or the objects of removal is greater than 10 xcexcm.
Solid substances or objects of removal are separated into pieces, as is sand. In order to form a film from the solid substances or the objects of removal, a support member must be placed below the film. For this reason, the first filter film is used as a support member, thus enabling formation of a second filter film over the first filter film. Further, so long as a pore formed in the first filter film is set to be greater in size than the smallest grain and smaller in size than the largest grain, large grains are first captured, and smaller grains are gradually captured later. Although the second filter film originally has apertures of large size, the filter yields an advantage of the ability to permit filtration of a fluid at a rate higher than that filtrated by a filter having apertures of small sizes.
The grain size distribution of the solid substances or the objects of removal shows two peaks, and the size of the pores of the first filter falls within the range between the two peaks.
Solid substances or objects of removal which are greater in size than the apertures of the first filter are present in greater proportion than are solid substances or objects of removal which are smaller in size than the apertures of the first filter.
Solid substances or objects of removal have a wide grain size distribution. Presence of solid substances or objects of removal of large sizes enables random formation of large apertures in the second filter film. Accordingly, a fluid can be filtrated at low suction pressure.
Preferably, after commencement of removal of objects of removal in a filtering process employing the first filter, a fluid is caused to circulate for a predetermined period of time.
After commencement of removal of objects of removal in a filtering process in which the first filter is used, a fluid is, in advance, caused to circulate for a predetermined period of time. As a result, the objects of removal are deposited on the surface of the first filter, thus forming a second filter film. Subsequently, the fluid is filtrated through the first and second filters. So long as the time during which a second filter film is formed as a result of circulation of a fluid can be determined, a second filter film can be formed through use of a timer after a new first filter film has been attached to a filtration unit, without involvement of a necessity for ascertaining formation of the second filter film. In the event of a clog arising in the filtration unit, the second filter film is removed together with the sediment formed on the filter film, and a fluid is caused to circulate, thus enabling automatic recovery of the second filter film. So long as the time required for collecting the second filter film through filtration of a fluid can be determined, the second filter film can be collected through use of a timer.
The degree to which the solid substances or the objects of removal still remain in the fluid that has passed through the first filter is detected by detection means. When the degree to which the objects of removal or solid substances are mixed in the fluid has reached a predetermined value or less, circulation of the fluid is stopped.
More specifically, after the degree to which the objects of removal are mixed in the fluid has reached a predetermined value or less, formation of a second filter film has been visually ascertained, and achievement of a sufficient filtrating effect has been found, circulation of the fluid is stopped, and the fluid is introduced into a filtration process, thereby enabling automatic recovery of the second filter film.
The degree to which the solid substances or the objects of removal still remain in the fluid that has passed through the first filter is detected by detection means. When the degree to which the objects of removal or solid substances are mixed in the fluid has reached a second predetermined value or more, circulation of the fluid is resumed.
Each aspect of the method described below is separately illustrative of the various embodiments of the invention and is not intended to be restrictive of the broad invention.
Namely, a first aspect of the method is a method of filtering a fluid, which comprises steps of:
preparing a filter containing solid substances differing from the objects of removal; and
filtering objects by supplying the fluid to the filter and thereby removing the objects of removables from the fluid.
A second aspect of the method is a method of filtering a fluid according to the first aspect, wherein the step of preparing a filter comprises a step of forming a second filter by depositing the solid on a first filter as a base.
A third aspect of the method is a method of filtering a fluid according to the first aspect, wherein said solid contains solid substances whose distribution of particle size is wider than that of the objects of removal.
A fourth aspect of the method is a method of filtering a fluid according to the first aspect, wherein the step of preparing a filter comprises steps of:
mixing a solid substance to the fluid containing objects of removal; and
forming a second filter by causing the fluid to pass through a first filter, to thereby constitute over the surface of the first filter a second filter containing the solid substances.
A fifth aspect of the method is a method of filtering a fluid according to the first aspect, wherein the step of preparing a filter comprises steps of:
mixing a solid substance whose diameter is larger than that of objects of removal to the fluid; and
forming a second filter by causing the fluid to pass through a first filter, to thereby constitute over the surface of the first filter a second filter containing the solid substances.
A sixth aspect of the method is a method of filtering a fluid according to the first aspect, wherein the step of preparing a filter comprises a step of:
forming a filter containing a solid substance whose composition is different from that of the objects of removal in the fluid.
A seventh aspect of the method is a method of filtering a fluid according to the first aspect, wherein the step of preparing a filter comprises the steps of:
mixing a solid substance whose composition is different from that of the objects of removal to the fluid; and
forming a second filter by causing the fluid to pass through a first filter, to thereby constitute over the surface of the first filter a second filter containing the solid substances.
An eighth aspect of the method is a method of filtering a fluid according to the first aspect, wherein the step of preparing a filter comprises the step of:
forming a second filter by immersing a first filter in a fluid containing a solid substance different from objects of removal to thereby constitute over the surface of the first filter a second filter containing the solid substances different from objects of removal; and
introducing a fluid containing objects of removal to the filter, thereby removing objects of removal contained in a fluid.
A ninth aspect of the method is a method of filtering a fluid, which comprises the steps of:
introducing a fluid containing objects of removal and solid substances differing from the objects of removal into a tank having a first filter;
causing the fluid to pass through the first filter, thereby constituting over the surface of the first filter a second filter containing the solid substances and eliminating the objects of removal from the fluid.
A tenth aspect of the method is a method of filtering a fluid according to the first aspect, wherein the fluid is acidic or alkaline, and a neutralizer is mixed into the fluid, thus neutralizing the fluid.
An eleventh aspect of the method is a method of filtering a fluid according to the first aspect, wherein the step of preparing a filter comprises a step of causing the fluid containing objects of removables to circulate through the filter or the first filter.
A twelfth aspect of the method is a method of filtering a fluid according to the second aspect,
wherein the filter or the second filter contains solid substances or objects of removal of different sizes.
A thirteenth aspect of the method is a method of filtering a fluid according to the second aspect, wherein the solid substances or the objects of removal contain particles of different sizes, and pores of the first filter are greater in size than the smallest grain and smaller in size than the largest grain.
A fourteenth aspect of the method is a method of filtering a fluid according to the second aspect, wherein the solid substances or the objects of removal contain flake state particles, and pores of the first filter are greater in size than the smallest grain and smaller in size than the largest grain.
A fifteenth aspect of the method is a method of filtering a fluid according to the second aspect, wherein the diameter of the smallest solid substance or objects of removal is less than 0.25 xcexcm, and the diameter of the largest solid substance or the objects of removal is greater than 10 xcexcm.
A sixteenth aspect of the method is a method of filtering a fluid according to the second aspect, wherein the grain size distribution of the solid substances or the objects of removal shows two peaks, and the size of the pores of the first filter falls within the range between the two peaks.
A seventeenth aspect of the method is a method of filtering a fluid according to the second aspect, wherein solid substances or objects of removal which are greater in size than the apertures of the first filter are present in greater proportion than are solid substances or objects of removal which are smaller in size than the apertures of the first filter.
An eighteenth aspect of the method is a method of filtering a fluid according to the first aspect, wherein said step of filtering comprises a step of circulating the fluid for a constant time since starting removing.
A nineteenth aspect of the method is a method of filtering a fluid according to the eighteenth aspect, wherein said step of circulating comprises a step of detecting an inclusion degree of removables included in the fluid passing through the filter, and stopping circulation of the fluid at the time when the inclusion degree has fallen bellow the predetermined value.
A twentieth aspect of the method is a method of filtering a fluid according to the nineteenth aspect, wherein said step of circulating comprises a step of detecting an inclusion degree of removables included in the fluid passing through the filter, and starting circulation of the fluid again at the time point when the detected degree exceeds a second constant value.
A twenty first aspect of the method is a method of filtering a fluid according to the nineteenth aspect, wherein said step of detecting comprises a step of detecting a transparence of the fluid by light sensor.
A twenty second aspect of the method is a method of filtering a fluid according to the first aspect, wherein said step of filtering comprises a step of filtering the fluid while sucking through the filter.
A twenty third aspect of the method is a method of filtering a fluid according to the twenty second aspect, wherein an applied suction pressure in sucking is within a range of 0.2 to 0.5 kg/cm2.
A twenty fourth aspect of the method is a method of filtering a fluid according to the second aspect, further comprising a step of applying an external force to a surface of the filter so that a constituent of the second filter can be moved.
A twenty fifth aspect of the method is a method of filtering a fluid according to the twenty fourth aspect, wherein said step of applying an external force comprises a step of applying the external force intermittently.
A twenty sixth aspect of the method is a method of filtering a fluid according to the twenty fourth aspect, wherein said step of applying an external force comprises a step of applying gas flow along a surface of the first filter.
A twenty seventh aspect of the method is a method of filtering a fluid according to the twenty fourth aspect, wherein said step of applying an external force comprises a step of applying a force so as to make a part of the constituent of the second filter released.
A twenty eighth aspect of the method is a method of filtering a fluid according to the twenty fourth aspect, wherein said step of applying an external force comprises a step of controlling a force so that a thickness of the second filter is constant.
A twenty ninth aspect of the method is a method of filtering a fluid according to the twenty fourth aspect, wherein said filter is disposed in perpendicular direction and said external force comprises a raising force of a bubble.
A thirtieth aspect of the method is a method of filtering a fluid according to the twenty fourth aspect, wherein said step of applying an external force comprises a step of applying a mechanical vibration.
A thirty first aspect of the method is a method of filtering a fluid according to the twenty fourth aspect, wherein said step of applying an external force comprises a step of generating a sonic wave.
A thirty second aspect of the method is a method of filtering a fluid according to the twenty fourth aspect, wherein said step of applying an external force comprises a step of generating a flow of the fluid.
A thirty third aspect of the method is a method of filtering a fluid according to the second aspect, wherein said first filter is made of polyolefin high polymer.
A thirty fourth aspect of the method is a method of filtering a fluid according to the second aspect, wherein said first filter has an uneven surface.
A thirty fifth aspect of the method is a method of filtering a fluid according to the second aspect, wherein said first filter has a bag typed filter in which clearance is formed and in which suction pipe for sucking is inserted.
A thirty sixth aspect of the method is a method of filtering a fluid according to the second aspect, wherein said second filter comprises at least one element of Si, SiGe, Al2O3, Si oxide, metal oxide, and IIa-VIIa, IIb-VIIb group of elements.
A thirty seventh aspect of the method is a method of filtering a fluid according to the second aspect, wherein said second filter comprises Si.
A thirty eight aspect of the method is a method of filtering a fluid according to the thirty seventh aspect, wherein said second filter comprises flake type of Si.
A thirty ninth aspect of the method is a method of filtering a fluid according to the second aspect, wherein said second filter comprises a mechanical processing waste generated in the mechanical processing step.
A fortieth aspect of the method is a method of filtering a fluid according to the thirty ninth aspect, wherein said mechanical processing step comprises a polishing step or grinding step.
A forty first aspect of the method is a method off filtering a fluid according to the thirty eighth aspect, wherein said mechanical processing waste is a waste of dicing.
A forty second aspect of the method is a method of filtering a fluid according to the forty first aspect, wherein said step of preparing a filter comprises a step of adding a flake shaped waste in to the fluid.
A forty third aspect of the method is a method of filtering a fluid according to the first aspect, wherein said fluid is fine particles wasted in a mechanical processing step.
A forty fourth aspect of the method is a method of filtering a fluid according to the first aspect, wherein said fluid is fine particles wasted in a CMP step.